Cold Spell Late Feb/ Early March Technical Discussion only MOD NOTE POST #1

sdanseo

Gaoth Laidir wrote: »

Snowfall in northern Germany today ranged from 2-7 cm, with liquid-equivalent ratios of around 25:1. Not as high as I had imagined for that area, so it begs the question what the ratio will be here. It is unlikely to be higher than that, and most likely lower, probably 15-20:1 initially anyway.

The snow depth forecast charts are based on a 10:1 ratio, so in reality they may be showing a little low. Having said that, I find it hard to believe we'll see 40 or 60 cm totals in places like Dublin. I reckon the highest depths reported at Dublin and Casement airports will be 15 cm.

Are you including Thursday-> Friday potential event in that prediction?

Daniel2590

GFS has the low ~300km further west than the 12z for 1am Saturday

NAGDEFI

GFS 18Z 120h the storm moving in from the south east. Better for snow as snowbie said. Less marginal.

ThaitaniumM

Large Funeral wrote: »

GFS 18Z 120h the storm moving in from the south east. Better for snow as snowbie said. Less marginal.

Not really, the Eastern flank is bringing up milder air

sdanseo

Daniel2590 wrote: »

GFS has the low ~300km further west than the 12z for 1am Saturday

Large Funeral wrote: »

GFS 18Z 120h the storm moving in from the south east. Better for snow as snowbie said. Less marginal.

850 temps struggling to -5 though. Would that be cold enough?

Kermit.de.frog

sdanseo wrote: »

850 temps struggling to -5 though. Would that be cold enough?

Still going for most Friday night.



An extraordinary potential amounts on this run.

Gaoth Laidir

Most snoefall is in the northwest quadrant of a low, so we want the low to be to our southeast, not southwest. Southwest means warn air advection over the country.

SleetAndSnow

this is taking a different path then ECM and UKMO, will it be an outlier and just a pub run? Sure hope so because the snow looks to be changed to rain and temps risen pretty quickly with this.

pad199207

This has all the hallmarks of going wrong for us too and not just for Southern England. People dismissing the milder air being brought into the mix is rather premature. Could turn out to be very marginal for South and East Coasts.

Fingers crossed this northward and westward trend stops in future model runs.

Gaoth Laidir

sdanseo wrote: »

Are you including Thursday-> Friday potential event in that prediction?

Sorry, I was referring to just the sea-effect showers.

snowstorm445

pad199207 wrote: »

This has all the hallmarks of going wrong for us too and not just for Southern England. People dismissing the milder air being brought into the mix is rather premature. Could turn out to be very marginal for South and East Coasts.

Fingers crossed this northward and westward trend stops in future model runs.

It is only the GFS which seems to be suggesting this, and a "pub run" at that. If it still appears tomorrow morning then I think we can be sure a definite trend is going on.

SleetAndSnow

this is taking a totally different path then the 12z, i watched the 150hr change from being over dublin to just being off the south west kerry coast.

ThaitaniumM

Scenario 1. Most favorable for Snow
Scenario 2. Favorable if it stalls then moves East or SE
Scenario 3. The least favorable as mild air will be pushed up through the Eastern Flank

sdanseo

pad199207 wrote: »

This has all the hallmarks of going wrong for us too and not just for Southern England. People dismissing the milder air being brought into the mix is rather premature. Could turn out to be very marginal for South and East Coasts.

Fingers crossed this northward and westward trend stops in future model runs.

There's very little difference in upper temps between the 12Z and 18Z. The leading edge could still be a full on blizzard.

Of course it could still all turn to rain.

The trend is good though is it not? If one run pushes it 300km northwest, the thing could be gone or sitting over the mid-atlantic by Tuesday's runs.

JCX BXC

Vast change on the 18z, this looks far from nailed.

patneve2

Gaoth Laidir wrote: »

Snowfall in northern Germany today ranged from 2-7 cm, with liquid-equivalent ratios of around 25:1. Not as high as I had imagined for that area, so it begs the question what the ratio will be here. It is unlikely to be higher than that, and most likely lower, probably 15-20:1 initially anyway.

The snow depth forecast charts are based on a 10:1 ratio, so in reality they may be showing a little low. Having said that, I find it hard to believe we'll see 40 or 60 cm totals in places like Dublin. I reckon the highest depths reported at Dublin and Casement airports will be 15 cm.

Important to note that the shower activity across N Germany occurred with pressure around or just below 1035 mb, hardly unstable conditions. Those accumulations are therefore promising from an Irish point of view imo.

Reckon your accumulation predictions are quite realistic. I reckon the convective event could bring anywhere between 12-20cm to Dublin/Casement. As for Friday, who knows.

George Sunsnow

pad199207 wrote: »

This has all the hallmarks of going wrong for us too and not just for Southern England. People dismissing the milder air being brought into the mix is rather premature. Could turn out to be very marginal for South and East Coasts.

Fingers crossed this northward and westward trend stops in future model runs.

I am trying to deal with that low as with how January 1982 went and with 1980’s experiences in my mind so I’m expecting it not to get as far north as some models are suggesting and therefore not injecting forward as much waa
I guess we’ll have to see what models do with it over the next 48hrs or so

SleetAndSnow

I still can't see how it can go to the southwest coast like that with the jet stream being so far south. I think this will be an outlier and the UKMO/ECM outlook will be a lot more likely, but the next runs should tell us that

NAGDEFI

ThaitaniumM wrote: »

Not really, the Eastern flank is bringing up milder air

Yeah needs to shift a little more east and south. Still it's a trend.

Snowbie

ThaitaniumM wrote: »

Not really, the Eastern flank is bringing up milder air

Not if it approached from SE as air be more or returning continental airmass. If it moved in from SW, more Atlantic influence with short spell of snow on its leading edge before martime air mixes. Regardless, as the fronts move through, uppers will warm but depends on direction of Lp how quickly they will warm will be determined by track. SE to NW will deliver substantial snow countrywide with little mixing in uppers keeping things right side of marginal for lot longer before sleety mess filters in.

ThaitaniumM

Take the 18Z with a pinch of salt though as it is probably an outlier. It will be interesting to see the 00Z and 06Z runs.

NAGDEFI

George Sunsnow wrote: »

I am trying to deal with that low as with how January 1982 went and with 1980’s experiences in my mind so I’m expecting it not to get as far north as some models are suggesting and therefore not injecting forward as much waa
I guess we’ll have to see what models do with it over the next 48hrs or so

I'd love to see the model output 4-5 days before 1982 commenced. This will go down to the wire.

Snowbie

ThaitaniumM wrote: »

Take the 18Z with a pinch of salt though as it is probably an outlier. It will be interesting to see the 00Z and 06Z runs.

Yup, stick with the midnight and noon runs from GFS in particular

Kermit.de.frog

The 18z GFS run shows 18 hrs of continuous snowfall for Dublin (and more for many other parts of the country) with sub zero DP and freezing temperatures.

Our standards seem to be a little high

Anyway still a lot to flesh out.

From now until then is completely nailed and those heavy snow showers will be coming on shore Tuesday afternoon.

Rougies

Gaoth Laidir wrote: »

Snowfall in northern Germany today ranged from 2-7 cm, with liquid-equivalent ratios of around 25:1. Not as high as I had imagined for that area, so it begs the question what the ratio will be here. It is unlikely to be higher than that, and most likely lower, probably 15-20:1 initially anyway.

The snow depth forecast charts are based on a 10:1 ratio, so in reality they may be showing a little low. Having said that, I find it hard to believe we'll see 40 or 60 cm totals in places like Dublin. I reckon the highest depths reported at Dublin and Casement airports will be 15 cm.

I find 15cm a rather conservative estimate. Any particular reason you don't think it will be higher?

As an example lets take the 48 hours from Tuesday evening to Thursday evening and assume the liquid-equivalent ratio averages 1:18 that would equate to just 8.3mm of precip for that duration. In an unstable flow with -12 ish uppers over an 8C Irish sea surely one would expect higher totals?

Of course the hit and miss nature of the showers will cause local variations, so 15cm is quite likely somewhere on the east coast but you seem to be suggesting that the highest (lowland) totals will be about that value?

JanuarySnowstor

Snowbie wrote: »

Yup, stick with the midnight and noon runs from GFS in particular

I often here this line about the gfs but find little justification for it....I've seen several times where the 18z picks up a new and correct trend.

I also find the gfs ppm charts very accurate while some think there a load of rubbish

NAGDEFI

I suppose we must remember that practically all the really huge snowfall events were marginal Bar Tue-Thur of Jan 1987. But a lot of the 1947 falls were.

We'll enjoy until Thursday. Not often we have snow guaranteed for much of the country for 48-72 hrs.

tayto lover

Did anyone hear anything about snow being expected?

Daniel2590

tayto lover wrote: »

Did anyone hear anything about snow being expected?

Nah not a thing, normal spring weather ahead

pistolpetes11

Annoyingly enough I have had to start giving out warnings for Off Topic posts on this thread once again please read below

Well it looks like we are set for quite the cold spell :D:D

This forum gets extremely busy during these weather events and for the most parts the thread are really enjoyable and you will garner lots of knowledge.

Although before you start posting we would like to summarise a few house rules here :

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There are a few threads in operation for this event

• The Main Discussion thread for the event
• https://www.boards.ie/vbulletin/showthread.php?t=2057843266
  
• The Technical Discussion Thread ( Please don't post in here if you’re looking to tell us its snowing or you want to know will it snow in your back yard )
• https://www.boards.ie/vbulletin/showthread.php?t=2057844498
  
• The FI Thread ( This is usually for charts that are 120 hours or more away )Although a lot of these charts will probably end up in the technical discussion thread anyway
• https://www.boards.ie/vbulletin/showthread.php?t=2057782713
  
• This thread below is a great resource for finding out where all the weather charts we use coming from and what they mean
• https://www.boards.ie/vbulletin/showthread.php?t=2056531638
  
• The Snow weather preparations - your lists, must dos and driving tips Thread
• https://www.boards.ie/vbulletin/showthread.php?t=2057844895
• And last but not least and perhaps the most important :eek: Our resident boards.ie forecaster MT's thread can be located in the link below
• https://www.boards.ie/vbulletin/showthread.php?t=2055579971&page=119

PLEASE FAMILIARISE YOURSELF WITH THE FORUM RULES IN THIS LINK



https://www.boards.ie/vbulletin/showthread.php?t=2056531690